The present invention relates generally to a heat exchanger for use with the primary heat exchanger of a condensing furnace or the single heat exchanger of a mid-efficiency furnace which includes a layer of oxidized black coating which increases the emissivity of the heat exchanger and allows the heat exchanger to emit more heat.
A condensing furnace generally includes two heat exchangers, a primary heat exchanger and a condensing heat exchanger. Air and natural gas enter a burner where they are burned to form hot combustion products. The primary heat exchanger cools the hot combustion products, extracting and supplying heat to the air that is to be heated. A standard (“mid-efficiency”) furnace generally includes only a single heat exchanger which cools the hot combustion products, extracting and supplying heat to the air to be heated.
These heat exchangers are commonly formed of a shiny aluminized steel. As the aluminized steel is shiny, the steel does not radiate heat well and has a low emissivity. Emissivity is the ability of a surface to emit heat by radiation. For example, black bodies have a higher emissivity than lighter bodies and are therefore able to emit more heat by radiation than lighter bodies.
There are several drawbacks to the aluminized steel heat exchanger of the prior art. For one, aluminized steel is expensive. Additionally, as the aluminized steel has a low emissivity, the steel does not radiate heat well.
Hence, there is a need in the art for a furnace heat exchanger which increases the emissivity of the heat exchanger and allows the heat exchanger to emit more heat.